Rapid thermal process (RTP) chambers need to control the power applied to a lamps when processing semiconductor wafers to control the amount of heat generated by the lamps. Current RTP chambers use a lamp driver circuit that includes a phase angled controlled silicon controlled rectifier (SCR) to control the power applied to a lamp to control wafer processing. These SCR based lamp driver circuits suffer from a number of drawbacks that limit the efficiency of wafer processing. One series drawback of the SCR based approach is that the power factor of the circuit is low. This is especially true at low power levels, where the power factor can be less than 50%. This makes semiconductor processing energy inefficient.
Additionally, the SCR based lamp driver circuit cannot be turned on near the points where voltage crosses zero. This is because an SCR requires a minimum voltage to be turned on. Therefore, the minimal value of controlled output current has a threshold. This also contributes to processing inefficiencies.
Another problem is that, because of the nature of a SCR, it can only be switched on and off two times per period. This is because the SCR switches off only when the current through the device is zero. High speed, temperature processing would be improved if more accurate control over a lamp driver circuit could be achieved.
Accordingly, in view of these drawbacks associated with SCR based lamp driver circuits in RTP chambers, new and improved lamp driver circuits are needed